I've got the same alternator with the same problem, haven't done anything about it yet, I suspect either it doesn't put out it's rated power or there is most likely a diode with a temp related problem. In cold winter weather it's just fine even with the engine coolant temp up to 195, but as summer comes on it starts out just fine but once the engine gets to 195 it craps out. The hotter the weather the sooner it stops producing power. It will hold 12 volts with the engine turning 2000 RPM but as soon as I hit city stop and go traffic and the cooling fans come on the voltage drops under 12. So I think I'll be shopping for a replacement before too long.